The cycloolefin-based copolymer has excellent characteristics such as high transparency (for optical applications), low photoelasticity (birefringence is not readily caused by external stress), good dielectric property (for a condenser dielectric body), low water-absorbance, high softening temperature (particularly, when the content of cycloolefin is large) (for high-temperature applications), and high vapor barrier property (for the packaging film field). In general, the cycloolefin-based copolymer is often synthesized under the presence of methallocene catalysis and production methods thereof are described in, for example, Patent Document 1, Patent Document 2, and so forth.
With respect to the molded body in which the cycloolefin-based copolymer is used such as a film, a cast film of ethylene-norbornene copolymer is described in Patent Document 3 and Patent Document 4. And, a film made of cycloolefin-based copolymer such as norbornene copolymer is described in Patent Document 5. And, a sheet of a semicrystalline cycloolefin copolymer is described in Patent Document 6. And, a film of cycloolefin copolymer is disclosed in Patent Document 7. And, a film having high rigidity based on a cycloolefin copolymer is disclosed in Patent Document 8. However, cycloolefin-based copolymers have the tendency that defects, also called fish eyes, due to gel particles, easily occur in molding. The copolymer has the problems that the defects inhibit the performance of the molded body, and utilization thereof is restricted.    Patent Document 1: EU Patent Publication No. 0503422    Patent Document 2: EU Patent Publication No. 0946618    Patent Document 3: DE Patent Publication No. 224538    Patent Document 4: DE Patent Publication No. 241971    Patent Document 5: EU Patent Publication No. 0384694    Patent Document 6: EU Patent Publication No. 0610814    Patent Document 7: EU Patent Publication No. 0610815    Patent Document 8: EU Patent Publication No. 0610816